[jdk11u-dev] RFR: 8275610: C2: Object field load floats above its null check resulting in a segfault

[Goetz Lindenmaier]

I backport this for parity with 11.0.15-oracle.

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Commit messages:
 - Backport 7c6f57fcb1f1fcecf26f7b8046a5a41ca6d9c315

Changes: https://git.openjdk.java.net/jdk11u-dev/pull/773/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk11u-dev&pr=773&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8275610
  Stats: 112 lines in 2 files changed: 112 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk11u-dev/pull/773.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk11u-dev pull/773/head:pull/773

PR: https://git.openjdk.java.net/jdk11u-dev/pull/773